Metal fiber composites



May 5, 1970 A. D. SCHWOPE E L 3,510,275

METAL FIBER COMPOSITES Filed Sept. 18, 1967 :s Sheets-Sheet 1 FIG.|

INVENTORS ARTHUR D.SCHWOPE ROBERT W. JECH BY EDWARD P. WEBER ATTORNEYMay 5, 1970 A. D. SCHWOPE ET AL 3,51 ,2

METAL FIBER COMPOSITES Filed Sept. 18, 1967 3 Sheets-Sheet :2

SI 2 vol FIBER IIIIIIIII 55.6 VOI. FIBER 30 Ovo|./ FIBER T46 vol4/oFIBER TENSILE STRENGTH (X I000 psi) MATRIX l UNALLOYED TI 0 200 400 600800 I000 I200 I400 TEMPERATURE F F l G 2 I I I I I 6 so .g 0 so o 9 50 X40 20vo1.%F11aER 5 MI E F- 20 ovo1.% FIBER I. 10 vol.% FIBER 5 MATRIXUNALLOYED Ti lo I l I I I 0 200 400 600 800 I000 I200 IN V EN TOR-E5ARTHUR D. SCHWOPE TEMPERATURE "F ROBERT W.JECH

BY EDWARD P. WEBER Fl G .3

ATTORNEY May 5, 1970 Filed Sept. 18, '19s? FIG.4

MODULUS OF ELASTICITY TO DENSITY RATIO (x I07) A. D. SCHWOPE ETAL METALFIBER comrosnns 3 Sheets-Sheet 3 MODULUS OF ELASTICITY (XIO psi) 3 E5MATRIXI l I I I I I I I TEMPERATURE F MATRIXI Ti 6Al-4V (0vo|.% FIBER) II I I I I I 40 voI./ FIBER FIG.5

INVENT0R ARTHUR 0. SCHWOPE TEMPERATURE F- I200 I600 ROBERT W. JECHEDWARD P. WEBER ATTORNEY United States Patent 3,510,275 METAL FIBERCOMPOSITES Arthur D. Schwope, 2501 Guilford Road, Cleveland Heights,Ohio 44118; Robert W. .Iech, 1598 Woodward Ave., Lakewood, Ohio 44107;and Edward P. Weber, 6943 York Road, Parma, Ohio 44130Continuation-impart of applications Ser. No. 822,838, June 25, 1959, andSer. No. 315,564, Oct. 11, 1963. This application Sept. 18, 1967, Ser.No. 672,415

Int. Cl. B22f 7/00; B23p 17/00 US. Cl. 29182.2 7 Claims ABSTRACT OF THEDISCLOSURE A composite metal structure of a powder metal matrix and aplurality of discrete metal fibers of a different metal distributedthrough said powder matrix. The matrix metal in powder form beingcombined, pressed, solid state sintered and worked to produce thecomposite. The fibers being composed of a metallic material havingsuitable characteristics for imparting an increase in strength to thecomposite over the strength of the matrix and arranged in the matrixwith their major axes oriented substantially in a single direction.

This application is a continuation-in-part of applica tions Ser. No.822,838, filed June 25, 1959 and Ser. No. 315,564, filed Oct. 11, 1963,both now abandoned.

This invention relates to a composite metal structure composed of apowder metal matrix reinforced with discrete metal fibers.

The alloying of elemental metals, metalloids, and nonmetals to achieveproperties not possessed by the individual constituents is, of course, avery ancient art and is by far the most common means for achieving thisresult. However, the advent of or rapid development in such fields asatomic energy, rocket propulsion, guided missiles, and supersonic speedaircraft has created stringent requirements for metals having uniquecombinations of properties such as, for example, lightness in weightcoupled with oxidation resistance and high temperature strength. In manycases it is impossible to attain the desired combinations of propertiesby means of conventional alloying procedures and, where possible, it isfrequently economically unfeasible or otherwise impractical to do so.

In the prior art it has already been recognized that some benefit can bederived from a structure consisting either entirely of metal fibers, orin which a self-containing fiber mass is infiltrated by another metal.In such a structure the fibers are usually mechanically interlocked andnot arranged in any particular direction. This concept has been utilizedprimarily to provide a porous body. However, the invention disclosedherein relates to a composite in which the fibers are without anystructural rigidity apart from the matrix. There is no mechanicalinterlocking and, moreover, it is preferred that at least the majorityof fibers do not touch each other to minimize stress concentrationeffects. The instant invention provides a structural material exhibitingimproved strength over and above the strength of the matrix, forinstance tensile strength and the modulus of elasticity, as hereafterfurther described.

It is believed that these advantages are at least in part achieved dueto the bond between the fiber and the matrix, the discreteness of thefiber and the unidirectional arrangement of the fibers. It is, ofcourse, a requisite that the fibers have the preferred properties, suchas tensile strength and modulus of elasticity, which are to be impartedto the matrix.

3,510,275 Patented May 5, 1970 "ice It is a fundamental object of thepresent invention to overcome at least one of the disadvantages and/0rlimitations of the metallurgical art as outlined above.

More specifically, it is an object of the invention to provide novel,composite metal structures which exhibit highly desirable specificproperties and/ or combinations of properties.

A particular object of the invention is the provision of light-weight,corrosion-resistant metal structures having good high temperaturestrength.

A further object is the provision of improved methods for producingcomposite metal structures.

Another aspect of the present invention resides in the provision of acomposite metal structure which consists of a powder metal matrix and aplurality of discrete fibers composed of another metal and runningthrough the matrix and solid state bonded thereto without structuralrigidity in the fiber mass independent of the matrix. The fibers are inthe form of whiskers and have, generally, a diameter of less than 0.10inch and are composed of a metallic material capable of imparting anincrease in strength to the composite over the strength of the matrix.The fibers are arranged in the matr'nr with their major axes orientedsubstantially in a single direction.

Additional objects of the invention, its advantages, scope, and themanner in which it may be practiced will be apparent to those conversantwith the art from the following description and subjoined claims taken';in conjunction with the annexed drawing in which:

FIG. 1 is a perspective elevational view, partly in section,diagrammatically illustrating the method and articles contemplated bythe invention; and

FIG. 2, 3, 4 and 5 are graphic presentations of properties of metalstructures according to the invention.

For the sake of example and literary ease the invention will bedescribed in detail as applied to a titanium matrix and molybdenumfibers; however, it will be appreciated that a wide variety of metalsand alloys and combinations thereof can be employedto obtain compositeshaving particular properties or sets of properties.

The metallic structures embraced by the invention are bodies (e.g.,rods, bars, plates, etc.) of a matrix metal, titanium in the exemplaryembodiment, containing fibers of a metal (e.g., molybdenum) possessingproperties which it is desired to impart to the matrix metal.

The structures fall into two general categories hereinafter referred toas the long fiber type and the short fiber type. It is pointed out thatthe terms long and short are used relative to each other and allude tothe length of the fibers, not in the completed structure but at thestart of its fabrication.

As used herein, the term fiber is employed and intended to embrace smalldiameter filaments ranging up to a maximum initial diameter of about0.020 inch. Theoretically there is no minimum diameter for the fibersemployed in short fiber composites; however, in practice, the thinnestfilaments would have a diameter in the order of a few microns or less.In the long fiber composites the minimum diameter would be dictated bythe need to handle and position individual fibers as will be seen asthis description proceeds.

The fibers employed in structures on which data are given herein were ofcommercially available electroetched, mechanically straightened 0.010inch diameter molybdenum wire.

Considering first the long fiber type structure, the physicalconfiguration of the composite will be more readily appreciated from thefollowing description of an exemplary manner of its fabrication.

The fibers are axially disposed in a clean mild steel tube one end ofwhich is then crimped shut on the wires and Welded. The tube then isfilled with matrix metal, in powder form. Preferably, the tube isvibrated to insure that the powder is well tamped down around the wires.After filling, the open end of the tube is crimped and welded closed onthe free ends of the Wires thus sealing the assembly and maintaining thewires running axially through the tube. The tube is then heated androlled in rod rolls. Working temperatures in the range of about 1450 to1800 F. give good results for titanium matrix with molybdenum fibers,with the lower temperatures used as the piece is progressively reduced.For different combinations of metals working temperatures suited to theparticular materials would be employed but care must be taken that theWorking temperature will not cause the powder nor the fibers to changeinto a liquid or semiliquid state.

A solid state bond is preferred since the mechanical properties of thefibers are usually detrimentally affected by contact with molten matrixmaterials. Placing the fibers in a liquid or semi-liquid state willcause all advantageous mechanical properties to be lost.

After reducing the diameter of the tube by about 75 to 99 percent, thejacket is stripped and the unclad rod cold rolled to improve the surfacefinish.

The reduction of the piece is efiective upon the fiber as well as thematrix material. Consequently, the finished structure comprises acompacted matrix with a multitude of very thin fibers extending throughthe body in one direction and individually bonded to the matrix.Inasmuch as the long fiber composites comprise continuous,unidirectionally oriented fibers, they exhibit anisotropic properties.This must be taken into account in the design of articles to befabricated from the material. In addition, this characteristic may beemployed to improve the isotropy of matrix materials which are naturallyanisotropic.

The significant improvement in tensile strength exhibited by the longfiber structure will be seen by reference to FIG. 2. It will be notedthat the degree of improvement is progressively more pronounced withincreasing temperature. In addition the tensile strength varies directlyWith the volume percentage of fiber in the structure.

It is believed that the marked improvement in the composites is due atleast in part to the fact that, at a given working temperature, one ofthe materials, e.g., the matrix is hot worked whereas the fiber is coldworked or vice versa.

While the improvements in properties achieved by long fiber typestructures are satisfactory, the fabrication techniques are somewhatfussy with regard to the arrangement of the fibers. However, it has beendiscovered the short fibers, randomly oriented, provide substantiallyequivalent results and, because the fabrication procedures are muchsimpler, these are preferred.

In a preferred method of fabricating the short fiber type structure,short fibers, e.g., in the order of 0.1 to 0.25 inch in length areadmixed and blended with the matrix powder. At this stage, the fibersare oriented at random. The blended powder then is compacted and vacuumsintered. The sintered billets then are canned and extruded into rod asshown schematically in FIG. 1. In this figure, designates a conventionalextrusion die, and 12, 12' a pair of rod rolls. The billet 14 enteringthe die is shown to contain randomly oriented fibers 16. In the extrudedrod 14a leaving die 10 and prior to entering rolls 12, 12' fibers 16have partially assumed a unidirectional orientation. The fibers in thefinished section 14b of the rod emerging from rolls 12, 12' aresubstantially unidirectionally oriented. Of course in actual practicethe fibers are not completely and perfectly reoriented but theproportion and degree of unidirectional orientation is quite high andefiective. It should be noted that FIG. 1 is an entirely schematicrepresentation of one exemplary type of working technique. Actually,this working would be a two step operation. Moreover, a wide variety ofworking methods can be employed, e.g., forging, swaging, rolling,extrusion, direct rolling of powder, etc.

While the process parameters employed are not critical and vary with theparticular materials operated upon, following are process details forthe specimens on which data are given hereinafter.

The fibers consisted of 0.010 inch diameter molybdenum wire varying inlength from 0.1 to 0.25 inch. The matrix powder was unalloyed titaniumor Ti-6Al-4V alloy. The billets were compacted at 70 tons per squareinch, vacuum sintered for one hour at 1800 F., canned in mild steel andextruded to /8 inch rod at 1800 F. The case was stripped (although itcan be left on) and the extruded rod re-canned in a stainless steeltube, heated to 1450 F. and hot rolled to A1. inch diameter.

The cladding was then removed and the rod cold worked to /8 inchdiameter followed by a two hour anneal at 1350 F.

FIG. 3 demonstrates the improvement in the tensile strength ofrespective short fiber type structures of unalloyed titanium containing10 to 20 volume percent molybdenum fiber as compared with a controlspecimen of the same material subjected to the same fabricationconditions but containing no fiber. It will be readily apparent frominspection of FIGS. 2 and 3 that the properties of the matrix materialare improved by the addition of either continuous or discontinuousfibers. In comparing FIGS. 2 and 3 it should be noted that, while thematrix material in each case was unalloyed titanium, it varied in thedegree of purity; this accounts for the difference in the tensilestrength of the control specimens containing no fiber.

Another important property of structural metals is the modulus ofelasticity. The improvement in this parameter exhibited by compositestructures comprising a Ti-6Al-4V alloy matrix, respectively, 20, 30,and 40 volume percent of discontinuous molybdenum fibers as comparedwith a control specimen of the same alloy as shown in FIG. 4. It will benoted that the modulus of elasticity increases directly with the volumepercent of molybdenum fiber. In addition the relationship of the modulusto temperature is generally linear up to 1400 F. whereas for thespecimen containing no fiber it drops off rapidly above about 600 F.

The effect of various volume percentages of molybdenum fiber (20, 30 and40%) on the modulus of elasticity to density ratio of Ti-6Al-4V alloyover a range of temperatures is shown in FIG. 5.

From the FIG. 5 curves it will be evident that structures containing atleast 20 volume percent molybdenum fiber have a notable advantage overthe specimen with no fiber with respect to modulus to density ratio attemperatures above about 400 F.; with 30 volume percent fiber, theadvantage exists at temperatures above F.; and with 40 percent fiber,the advantage is much greater and is manifested at all temperatures.

To obtain the fullest benefits of the molybdenum fibers at hightemperatures the composites may be suitably coated or other meansemployed to prevent oxidation of the fiber. This is true of any fibermaterial which tends to oxidize readily under conditions of use.

As previously explained, the invention is applicable to a wide range ofdifferent metal matrixes and fibers which are not physically orchemically incompatible with each other or with the fabricationtechniques involved. Thus, the matrix metal must be one which issusceptible of being formed by powder metallurgy or must have asubstantially lower melting point than the fiber; the fiber metal mustbe susceptible of being formed as a thin filament, and of bonding to thematrix metal with the application of heat and pressure. Of course, thefiber metal should possess some property or properties which it isdesired to impart to the matrix. In some cases it may be necessary toemploy fibers of two or more different materials to achieve the desiredresult.

While there have been described what at present are believed to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is aimed,therefore, to cover in the appended claims all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A composite metal structure comprising: a powder matrix of one metaland a plurality of discrete fibers of at least one other metal runningthrough said matrix and solid state bonded thereto without structuralrigidity in the fiber mass independent of the matrix, said fibers havinga diameter of less than 0.10 inch and being composed of a metallicmaterial efiective for imparting an increase in strength to thecomposite over the strength of said matrix, said fibers being arrangedin said matrix with their major axes oriented substantially in a singledirection.

2. A composite metal structure according to claim 1, wherein said fiberscompose from about 3 to 60 percent of the volume of said structure andeach individual fiber is continuous throughout the matrix.

3. A composite metal structure according to claim 1, wherein said fibersare discontinuous and short in comparison to any major dimension of saidstructure and constitute about 3 to 60 percent of the volume of saidstructure.

4. A composite metal structure comprising: a matrix composedpredominantly of powdered titanium and having distributed uniformlytherethrough a plurality of discontinuous and discrete filamentaryfibers composed of molybdenum without structural rigidity in the fibermass independent of the matrix, said fibers being individually solidstate bonded to said matrix and arranged therein with their major axesoriented substantially in a single direction.

5. A composite metal structure according to claim 4, wherein saidmolybdenum fibers constitute 3 to 60 percent of the volume of thestructure and are less than 0.01 inch in diameter.

6. A composite metal structure comprising: a matrix composedpredominantly of powdered titanium and having uniformly distributedtherethrough a plurality of discontinous discrete fibers composed ofmolybdenum and having a length of 0.10 to 0.25 inch and being of 0.01inch in diameter and solid state bonded to said matrix, said fibersconstituting about 3 to percent of the volume of said structure withoutproviding structural rigidity in the fiber mass independent of thematrix, said fibers being arranged in said matrix with their major axesoriented substantially in a single direction.

7. In an elongated composite structure of a metallic matrix containing areinforcing metal having a tensile strength greater than that of saidmatrix; the improvement comprising a plurality of discontinuous fibersof said reinforcing metal dispersed within and solid state bonded tosaid matrix with their longitudinal axes substantially parallel to thelongitudinal axis of said structure, each of said fibers having adiameter less than about 0.010 inch and length within the range fromabout 0.1 to about 0.25 inch.

References Cited UNITED STATES PATENTS 1,704,256 3/ 1929 Lorenz -2002,455,804 12/1948 Ransley et a1. 75--200 3,047,383 7/ 1962 Slayter29182.5 3,114,197 12/1963 Du 'Bois et a1. 75200 3,177,578 4/1965 Barr75200 3,254,189 5/1966 Evanicsko et al. 75200 3,285,825 11/1966 Jens176-90X 3,337,337 8/1967 Weeton et al. 29-419X FOREIGN PATENTS 749,66911/ 1944 Germany. 706,486 3/ 1954 Great Britain.

BENJAMIN R. PADGETT, Primary Examiner A. I. STEINER, Assistant ExaminerU.S. Cl. X.R. 29-1823, 419

